1. Field of the Invention
The invention relates to a gas and steam turbine system, with a steam generator connected downstream of a gas turbine on the exhaust gas side for producing steam for a steam turbine in a water-steam loop, in which the steam generator includes a furnace system connected downstream of a coal mill.
In the planning and construction of a gas and steam turbine system, and especially when a gas turbine system is coupled to an existing steam turbine system with a furnace system, the mutually dependent capacities of the gas turbine and the steam turbine and also of the steam generator must be adapted to one another in order to attain high overall total efficiency. The total efficiency becomes higher as the gas turbine is operated longer at full load. However, since in such a system the exhaust gas of the gas turbine is typically used as combustion air for the furnace system of the steam generator, any change in the steam generator capacity, instance from a reduction in the flame temperature of the furnace system, results in an incorrect ratio between the quantity of gas turbine exhaust gas and the requisite quantity of air or oxygen of the furnace system. As a result, the efficiency of the system can be optimized only to a limited extent, especially in the partial-load range.
2. Summary of the Invention
It is accordingly an object of the invention to provide a gas and steam turbine system, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type and which attains the highest possible total efficiency in all operating states, when retrofitting an existing steam turbine system by adding a turbine. Maximal utilization of existing component assemblies should be permitted in the process.
With the foregoing and other objects in view there is provided, in accordance with the invention, a gas and steam turbine system, comprising a coal mill; a steam turbine having a water-steam loop; a gas turbine having an exhaust gas side supplying exhaust gas; a first heat exchanger connected to the exhaust gas side of the gas turbine; a steam generator connected downstream of the exhaust gas side of the gas turbine and upstream of the steam turbine in the water-steam loop for generating steam for the steam turbine, the steam generator having a furnace system connected downstream of the coal mill for supplying flue gas flowing through the steam generator; a second heat exchanger connected to the coal mill; means for delivering a first adjustable fractional quantity of the exhaust gas from the gas turbine after being cooled in the first heat exchanger, to the furnace system as combustion air; means for delivering a second adjustable fractional quantity of the cooled exhaust gas to the second heat exchanger for heating air for the coal mill; and means for admixing a third adjustable fractional quantity of the cooled exhaust gas with the flue gas from the furnace system.
In accordance with another feature of the invention, in order to produce additional steam for the steam turbine, the heat exchanger through which the exhaust gas from the gas turbine flows is connected into the water-steam loop of the steam turbine. The exhaust gas from the gas turbine is advantageously cooled to the highest temperature permitted by the structure of the existing flue gas conduits of the gas turbine system.
In accordance with a further feature of the invention, in order to enrich the combustion air for the furnace system with oxygen, a fraction of the air heated in the second heat exchanger is delivered to the first fractional quantity of the cooled exhaust gas.
In accordance with a concomitant feature of the invention, in order to regulate the temperature in the coal mill, cold air is admixed with the air heated in the second heat exchanger for the coal mill.
The advantages attained with the invention are particularly that on one hand by cooling down the exhaust gases from the gas turbine in a heat exchanger, overheating of existing flue gas conduits of the gas turbine system is reliably avoided, and on the other hand, by splitting the cooled exhaust gases into regulatable fractional quantities, additional utilization of the heat contained in the exhaust gases for the total process and therefore a high total efficiency of the system regardless of the operating state are attained.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a gas and steam turbine system, it is nevertheless less not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.